The present invention relates to a variable displacement compressor having single-headed pistons, which is used, for example, in a vehicular air conditioning system.
A variable displacement swash plate clutch compressor shown in FIG. 8 has a solenoid clutch 101, which can interrupt power transmission from a vehicular engine Eg. The compressor also has a displacement control mechanism, which can reduce the displacement so that the solenoid clutch is not be turned on and off frequently when the cooling load is low.
The displacement control mechanism has a swash plate 103 connected to pistons 102 through shoes 102a. A rotary support 105 is fixed to a drive shaft 104. The swash plate 103 is connected to the rotary support 105 through a hinge mechanism 106. The swash plate 103 is housed in the crank chamber 107. The differential pressure between the crank chamber 107 and the cylinder bores 18 varies to change the inclination angle of the swash plate 103. As the inclination angle of the swash plate 103 is changed, the stroke of each piston 102 is changed to change the displacement.
For example, when the pressure of the crank chamber 107 is increased to increase the difference between the pressure of the pressures of the cylinder bore 108, the inclination angle of the swash plate 103 is reduced, which reduces the compressor displacement. In FIG. 8, the swash plate 103 indicated by the broken double-dashed line is at the minimum inclination position, where it abuts against a regulating ring 109 attached to the drive shaft 104. When the internal pressure of the crank chamber 107 is reduced to reduce the differential pressure the cylinder bores 108, the inclination angle of the swash plate 103 is increased to increase the compressor displacement.
Generally, in the step of compressing a refrigerant gas, the piston 102, the swash plate 103, the hinge mechanism 106, the rotary support 105 and the drive shaft 104 transmit force to the internal wall surface of a housing 110 (leftward in FIG. 8) through a thrust bearing 111 due to the compression load on the piston 102.
The internal pressure of the crank chamber 107 remains high so that the compressor can be started from the minimum displacement state, at which the load torque is minimized, even if the solenoid clutch is turned on soon after it is turned off. Further, control of the compressor displacement is performed to minimize the displacement, regardless of the cooling load, to reduce load of the engine Eg during rapid acceleration of the vehicle.
When the internal pressure of the crank chamber 107 is increased rapidly to minimize the displacement, the swash plate 103 may be pressed against the regulating ring 109 with excessive force, or the rotary support 105 may be pulled strongly to the rear side of the compressor through the hinge mechanism 106. Thus, the drive shaft 104 is caused to slide or shift backward (rightward in FIG. 8) along the axis L.
Upon such movement of the drive shaft 104, the top dead center position of the piston 102 shifts toward the valve plate 112. Therefore, the piston 102 may impinge upon the valve plate 112 when reaching the top dead center position. This impingement causes vibrations and noise and may damage the pistons 102 or the valve plate 112.
Also, when such backward movement of the drive shaft 104 takes place when the solenoid clutch 101 is turned off, an armature 101a of the solenoid clutch 101 moves toward a rotor 101b to eliminate a clearance between the armature 101a and the rotor 101b or to bring the armature 101a into contact with the rotor 101b, which causes rattling or vibration and unnecessary power transmission.
To solve the above problems, a spring 113 is located between the housing 110 and the drive shaft 104. The spring 113 urges the drive shaft 104 axially forward.
Japanese Unexamined Patent Publication No. Hei 11-62824 discloses a compressor having a restricting member for restricting axial shifting of the drive shaft. The restricting member is located in a hole in which the rear end of the drive shaft is fitted. The hole communicates with a suction chamber through a space. A sealing member, which prevents communication between a crank chamber and the space through the hole is applied around the rear end of the drive shaft.
To securely prevent backward axial shifting of the drive shaft 104 shown in FIG. 8, it is essential to use a very stiff spring 113. As a result, the thrust bearing 111 receives a great load from the spring 113, which reduces the life of the thrust bearing 111 and increases the power loss of the compressor at the thrust bearing 111. The increased power loss adversely affects the fuel consumption rate of the engine Eg that drives the compressor.
In the compressor disclosed in Japanese Unexamined Patent Publication No. Hei 11-62824, a sealing member is located in the hole in which the rear end of a drive shaft is supported. The sealing member prevents entry of refrigerant into the hole. Therefore, lubricant cannot be supplied fully to the radial bearing, which shortens the life of the bearing.
It is an object of the present invention to provide a variable displacement compressor having a simple constitution and being capable of maintaining sufficient lubrication of the radial bearing.
To achieve the above objective, the present invention provides a variable displacement compressor. The compressor comprises a housing having a suction chamber and a discharge chamber. A crank chamber is defined in the housing. A drive shaft has a front end and a rear end. The shaft is supported in the housing so that the front end protrudes from the housing. A cylinder block forms part of the housing. Cylinder bores are defined in the cylinder block. A valve plate assembly includes a suction port, a suction valve, a discharge port and a discharge valve for each cylinder bore. Single-headed pistons are housed in the cylinder bores, respectively. A drive plate is housed in the crank chamber and is connected to the pistons to convert rotation of the drive shaft into reciprocating motion of the pistons. The drive plate rotates integrally with the drive shaft. A control mechanism controls inclination of the drive plate by controlling the pressure of the crank chamber to change the volume of a refrigerant discharged from each cylinder bore into the discharge chamber. A radial bearing supports the rear end of the drive shaft. The refrigerant flows through the radial bearing. A holding bore houses the rear end of the drive shaft and the radial bearing. The holding bore is connected to a holding space. The holding space is defined by the valve plate assembly. A passage connects the holding space and the suction chamber. A restricting member is located in the holding space. The restricting member restricts axial movement of the drive shaft and divides the holding space into a first region and a second region. The first region and the second region communicate with each other. A clearance is formed between the drive shaft and the restricting member or between the restricting member and the valve plate assembly in a normal compressing operation. The clearance disappears when the pressure of the crank chamber is increased rapidly by the control mechanism.
The present invention also provides a variable displacement compressor. The compressor comprises a housing having a suction chamber and a discharge chamber. A crank chamber is defined in the housing. A drive shaft has a front end and a rear end. The shaft is supported in the housing so that the front end protrudes from the housing. A cylinder block forms part of the housing. Cylinder bores are defined in the cylinder block. A valve plate assembly includes a suction port, a suction valve, a discharge port and a discharge valve for each cylinder bore. Single-headed pistons are housed in the cylinder bores, respectively. A drive plate is housed in the crank chamber and is connected to the pistons to convert rotation of the drive shaft into reciprocating motion of the pistons. The drive plate rotates integrally with the drive shaft. A control mechanism controls inclination of the drive plate by controlling the pressure of the crank chamber to change the volume of a refrigerant discharged from each cylinder bore into the discharge chamber. A radial bearing supports the rear end of the drive shaft. The refrigerant flows through the radial bearing. A holding bore houses the rear end of the drive shaft and the radial bearing. The holding bore is connected to a holding space. The holding space is defined by the valve plate assembly. The holding space is connected to the suction chamber. Means for restricting restricts axial movement of the drive shaft. The restricting means are located in the holding space and divides the holding space into a first region and a second region. A clearance is formed between the drive shaft and the restricting means or between the restricting means and the valve plate assembly in a normal compressing operation. The clearance disappears when the pressure of the crank chamber is increased rapidly by the control mechanism. A passage connects the first region to the second region.
The present invention also provides a variable displacement compressor. The compressor comprises a housing having a suction chamber and a discharge chamber. A crank chamber is defined in the housing. A drive shaft has a front end and a rear end. The shaft is supported in the housing so that the front end protrudes from the housing. A cylinder block forms part of the housing. Cylinder bores are defined in the cylinder block. A valve plate assembly includes a suction port, a suction valve, a discharge port and a discharge valve for each cylinder bore. Single-headed pistons are housed in the cylinder bores, respectively. A drive plate is housed in the crank chamber and is connected to the pistons to convert rotation of the drive shaft into reciprocating motion of the pistons. The drive plate rotates integrally with the drive shaft. A control mechanism controls inclination of the drive plate by controlling the pressure of the crank chamber to change the volume of a refrigerant discharged from each cylinder bore into the discharge chamber. A radial bearing supports the rear end of the drive shaft. The refrigerant flows through the radial bearing. A holding bore houses the rear end of the drive shaft and the radial bearing. The holding bore is connected to a holding space. The holding space is defined by the valve plate assembly. A passage connects the holding space and the suction chamber. A cylindrical body is located in the holding space. One end of the cylindrical body is fixed to the drive shaft, and the other end of the cylindrical body abuts against the valve plate assembly. The cylindrical body restricts axial movement of the drive shaft and divides the holding space into a first region and a second region. The cylindrical body has a hole to connect the first region to the second region. A clearance is formed between the drive shaft and the cylindrical body or between the cylindrical body and the valve plate assembly in a normal compressing operation. The clearance disappears when the internal pressure of the crank chamber is increased rapidly by the control mechanism.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of examples the principles of the invention.